Endoprosthetic components for fusing vertebral bodies are known. They are adapted, in terms of their geometry, to the anatomy of the human vertebral body, are located between two vertebral bodies and completely or partially replace the intervertebral disk
During a first phase of their duration in the human body, they typically keep the vertebral bodies at a distance and in an anatomically correct and neurologically optimal position solely by way of their mechanical properties (load-bearing capacity). In the embodiment as a cage, they promote fusion of a bone attached in or on the implant, and thus the adhesion of the two surrounding vertebral bodies in a second phase.
These known components for fusing vertebral bodies are based on metal materials, such as titanium or tantalum, plastic materials such as PEEK, or ceramic materials such as silicon nitride.
Disadvantages of metal materials are, for example:                Metallic abrasion and the resulting negative effects on the human organism, such as foreign body reactions including inflammatory or immunological reactions        Artifacts in imaging for medical diagnostics        Effects of aging and long-term performance (fatigue, corrosion, and the release of metal ions, which can be toxic)        
Disadvantages of plastics-based components, such as highly cross-linked PE materials or PEEK, can be as follows:                Insufficient mechanical properties, such as prongs or other elements of the component breaking off, for example during installation. This may adversely affect the human organism.        Lack of presentability in common imaging processes (MRI, X-ray), thereby requiring the use of metallic markers.        Effects of aging and long-term performance, in particular material fatigue.        
A fundamental problem that is increasingly becoming the center of attention in implantation operations is the risk of infection during surgery. This risk can be reduced with ceramic components, the surface properties of which may act in an inhibiting manner on bacteria colonization, for example.
Ceramic components based on silicon nitride, for example, are also known.
However, this class of materials was developed with a view toward excellent high-temperature properties—for example for machining of metal components for the automotive industry—and ranks more in the midfield compared to other oxidic system-based ceramic high-performance materials when it comes to the properties required for use as a medical implant, such as strength, hardness and long-term stability.
Moreover, this is a material that is composed of multiple components and comprises needle-shaped silicon nitride particles, embedded into a glass matrix. The sintering of the material is accordingly complex. Mechanical processing, such as grinding or polishing, is thereby likewise extremely demanding and difficult.
All of these disadvantages lead to increased costs in the production of the components, which constitutes a further drawback.
Moreover, components made from Si3N4 have a rather dark coloration—gray to black—which for purely visual and aesthetic reasons meets with a low level of acceptance in the medical field.
Known ceramic cages generally have an annular design or are adapted to the shape and anatomy of the human vertebral bodies, wherein the ring is composed of a monolithic, which is to say dense, firm and stiff ceramic material.
The center of these cages can have a cavity, which is either filled with (autologous, allogeneic or synthetic) known bone (substitute) materials or has an artificial porous osseoinductive or osseoconductive core structure, which in general is significantly less rigid than the outer ring. In this area, bone cells are intended to form new bone material, wherein the cells involved in this process require an appropriate mechanical stimulus.
A variety of different manufacturing approaches exists with respect to these core structures.
A direct replication technique based on polyurethane foams in combination with a special chemical vapor deposition (CVD) method for depositing tantalum is known from U.S. Pat. No. 5,282,861, for example. The method can be used to produce porous and interconnecting tantalum structures, see FIG. 1, which are to encourage new bone growth. The production process is highly complex, difficult to control and, due in no small part to the tantalum material that is used, also expensive.
What is essential is that interconnecting structures, which is to say open-cell structures, are formed, which contributes to the osseoconductive and osseoinductive nature of the structures produced therewith.
Based on the production process, the individual struts forming the pore-like cavities are composed as follows:
A carbon-containing structure is located at the center, which is created from the polyurethane foam by way of pyrolysis processes and, in the sectional view through the strut, has a triangular shape, see reference numeral 1 in FIG. 2.
Using a CVD method, tantalum is deposited onto these structures, whereby a coating 2 is formed.
The production of osseoconductive structures from ceramic materials is likewise known. One production option is to employ a foaming method in which air is introduced into a ceramic slip, and thus bubbles are created, using specially controlled processes. These structures have relatively high mechanical stability and load-bearing capacity, with compressive strengths in the double-digit megapascal range.
However, it is a disadvantage that no, or almost no, interconnectivity of the porous structures exists, and consequently an essential prerequisite for new bone growth is lacking.
Another variant for forming pores in ceramic structures in a targeted manner is based on the use of organic pore-forming agents, such as organic beads, which are deliberately introduced or applied during the course of the process and then, after burnout, create porosities, see DE 100 15 614 B4, for example.
This technique is suitable for creating rough surfaces. However, it is not suitable for producing components where bone ingrowth is desired since an appropriate interconnectivity of the pores is missing.